Porous substrates, including concrete, masonry and wood structures, are vulnerable to the general effects of weathering and specifically to exposure to water and oil. The weathering of concrete substantially shortens the useful life of structures such as highways, bridges, parking ramps and the like. Exposure of wood and masonry substrates to water and oil can also significantly shorten the useful life of the product and reduce its aesthetic appeal even before it is no longer functional. Such substrates are often sealed with a film-forming resin, such as an epoxy or urethane product. These coating materials are often quite expensive and may undesirably alter the appearance of the coated substrate. Such coatings also seal the product completely, preventing or greatly reducing the escape of moisture from the coated substrate.
Silane and siloxane compositions are commercially available to seal both wood and masonry substrates to provide protection against water damage, which are typically delivered from volatile organic solvents. These compositions are undesirable because of the adverse effects of the solvents upon the atmosphere and the resultant health problems associated with air pollution. For example, chlorinated hydrocarbon solvents have been shown to adversely effect the ozone layer. Other organic solvents such as aromatic solvents are undesirable because of their toxicity. Therefore, systems utilizing organic solvents are not desirable.
A number of water-dispersed or water-emulsified silane treatments have been developed in response to environmental concerns. Examples of such systems include those described in U.S. Pat. No. 4,648,904 to DePasquale, U.S. Pat. No. 4,517,375 to Schmidt and U.S. Pat. No. 4,661,551 to Mayer et al. DePasquale provides an aqueous emulsion of a hydrolyzable silane and an emulsifying agent having an hydrophilic-lipophilic balance (HLB) value from 4 to 15. Schmidt discloses aqueous impregnation solutions prepared from hydrolyzed alkyl trialkoxy silanes. Mayer et al. teach the use of a transparent organosilane composition which is easily dispersed in water to form a transparent microemulsion.
While providing ecological advantages over solvent-based treatments, these water-dispersed or water-emulsified silane materials have not been able to provide performance comparable to solvent delivered materials. Also, many of these silane/siloxane materials exhibit poor substrate penetration. Additionally, such silane materials may not exhibit oil repelling properties.
Silanes which contain fluorine, however, have been used as water and/or oil repelling agents in other applications such as oil repellents on automobile and aircraft windshields. For example, U.S. Pat. No. 3,427,336 to Tiers discloses the use of perfluorocarbon substituted organosilanes as oil, water and ketone repellents on glass. Similarly, U.S. Pat. No. 3,442,664 to Heine discloses an aircraft windshield treatment that contains a low molecular weight polymeric fluorine-containing organo-siloxane.
Thus, there currently exists a need for compounds which provide a satisfactory balance of water and oil repellency on porous substrates. More specifically, there exists a need for compounds which eliminate the adverse effects associated with solvent based treatments and which protect porous substrates from water, salt, waterborne chemicals, and oily stains such as motor oil or paints and paint films. In addition, there exists a need to apply this protection from an aqueous delivery system rather than from solvent.